SissySIT R.3

.......

And one more thing. I think that you ought to have a Thread/Sticky of pictures of builds your designs. They are sort of spread all over. Not sure if we should post to the "diy Pass Amplifier" thread. Although many amplifiers are derivative, Pics of Iron Pumpkin and or turtle should have there own home. Just sayin....

I have a place for that - my Blog, but somehow I must find the time to post sometimes :rofl:

regarding "what's so temp sensitive" - in this case , SIT Is biggest Brute in company

but, as I said - just chill

or in your case - guild the lily (for fun) and chill
 
Looking at how things might be laid out (at a single channel... donuts and PSU will be stacked).

I'm thinking of tapping holes for SIT in this general vicinity -- probably slightly more towards the center of the heatsink/chassis (a bit further away from donuts).

move Donut to left (corner) or stack it vertically (L Profile, wood construction elements) near front plate

SIT - good as is, or move it more centrally on its heatsink, if you dare to tap

arrange that holes are in between fins, so you can drill through-holes, tapping much less critical

feel free to leave just few mm between SIT and pcb, no danger there - as always - keeping it at 33% of heatsink height is proven recipe for best thermal arrangement

same applies to mosfet (33%) so I believe it's better to use other channel pcb in that position (so MOS is down, not up)

edit: in case that you're putting both channels in that case, it's certainly best to have Donut vertical

do anything you can to leave enough space for final fiddling with trimpots; fingers and small screwdriver ....... you must squeeze them in in the end
 
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Donuts, plural

it's going to be tight

well, more fun, indeed

trimpot screwdriver for ZM Level of Clumsiness (less harm if it falls somewhere, no shorts )
 

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sp33ls

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2018-04-06 7:09 pm
USA
Are these 4 taps towards the center supposed to line up with the PCB? Just ever so sightly off (can see left screw angled). Maybe my heatsink isn't mounted 100% correctly
PXL_20220424_021038700.MP.jpg


Edit: how critical is it that I lower the MOSFET from my previous picture? I've already tapped holes for one SIT in the previous configuration. Wondering if the MOSFET wouldn't be sufficiently cooled being 33% from top.
 
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sp33ls

Member
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2018-04-06 7:09 pm
USA
I think I'm just going to try for the original config I had posted.

Since it's dual mono in same chassis, I am wondering if I'd be separating left and right grounds sufficiently by lifting with CL60 (found this in another Pass FW thread). Hoping to avoid ground loops.
PXL_20220424_063704701.MP.jpg

Left terminal:
  • PSU PCB GND (left)
  • Left channel GND

Right terminal:
  • PSU PCB GND (left)
  • Left channel GND

Center terminal:
  • IEC inlet GND
  • both transformer shields
  • chassis

Would this work? Should I be separating PSU GND left/right, or would both go to center terminal instead?

Thanks again for any tips
 
Are these 4 taps towards the center supposed to line up with the PCB? Just ever so sightly off (can see left screw angled). Maybe my heatsink isn't mounted 100% correctly


Edit: how critical is it that I lower the MOSFET from my previous picture? I've already tapped holes for one SIT in the previous configuration. Wondering if the MOSFET wouldn't be sufficiently cooled being 33% from top.

yeah, 4 holes are aligned for UMS, so mount pcbs wherever you can

as shown, it's OK

if there is some misalignment, you need to loosen M4 heatsink screws and press them together, then tighten the screws

edit: or just widen the holes in pcb, don't be scared of that

4mm drill will do everything you need

don't touch hole where mosfet is, fix other 3
 
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I think I'm just going to try for the original config I had posted.

Since it's dual mono in same chassis, I am wondering if I'd be separating left and right grounds sufficiently by lifting with CL60 (found this in another Pass FW thread). Hoping to avoid ground loops.
View attachment 1047646

Left terminal:
  • PSU PCB GND (left)
  • Left channel GND

Right terminal:
  • PSU PCB GND (left)
  • Left channel GND

Center terminal:
  • IEC inlet GND
  • both transformer shields
  • chassis

Would this work? Should I be separating PSU GND left/right, or would both go to center terminal instead?

Thanks again for any tips

wire from first channel PSU GND-one end of NTC-chassis

wire from second channel PSU GND-one end of NTC-chassis

simple as that

channel pcb is getting GND from its PSU pcb, RCA GND goes to channel input GND pad

simple as that
 

sp33ls

Member
Paid Member
2018-04-06 7:09 pm
USA
Made decent progress this weekend. I expected to have completed it by this weekend, but ended up fighting with the heatsinks and placement of everything. Definitely gave myself a challenge by going with the new Monoblock lol. Trying to minimize any chance of hum the best I can.

Hopefully it'll be up and running next weekend, just need to grab a different length M4 for the Tokin, and may decide to re-tap for one channel for better placement.

This home stretch is the worst -- the anticipation of whether it'll fire right up, or catch fire itself... :flame:

PXL_20220425_050243794.MP.jpg


PXL_20220425_044541566.MP.jpg
 
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jcon2

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2004-04-14 8:14 pm
Seattle
They ain’t no Sissy’s . They be beasts.

Have been “Chillin” as per ZM recommendation and placed the Sissie’s in my main system. Was able to get the offset in the teens when at thermal stability and called it good. I generally have mild concerns about 20 wattish amps with the Harbeth 7ES-3’s as they are 86dB sensitivity. Concern was not warranted. Rest of system is Salas preamp DCG3 and Aurender A10. Had been running an F5 (not dual mono, but with Toshiba mosfets). Would seem that the Sissys’ have teeny bit less gain than the F5. Most listening at 1 o’clock on the DCG3. Also had the great fortune to be chosen in the lottery to buy and build an N-channel Sony Vfet (#143). Had this in the system and loved the expanded sound stage and “musicality”But there was Somewhat less control of bass and bit of drift on imaging. I have found the perfect home for it an another system with less demanding speakers and with the aid of sub. In my other system magic it is really magic.

I’m aware of my potential to overvalue my own projects (endowment bias). In this case I’m fine with the bias. More often than not have had experience of “Hmm was that worth it?” Not so in this project.


I have thought for the longest time that I have a difficult room that was causing me difficulty. 22 ft x 11ft x 7.5 ft. Image and bass were never quite right despite moving my speakers numerous times and a variety of electronics.

Things that were immediately apparent was great improvement in imaging/spatial localization of instruments. This was quite impressive with even modest volumes. (65dB-70dB). The ability to enjoy music at lower volume levels make the listening experience so much less fatiguing. Part of the imaging may simply due to the dual mono setup but I suspect maybe not. Definitely felt that the Sissy were in control and knew exactly what they wanted.

From first power up they were dead quiet at the speaker.

The width of sound stage and stability of image was impressive. The thing that impressed me the most was the accurate timbre of instruments. I have historically found a lot of jazz (particularly horns trumpet) to be a potentially difficult listen. The Sissys’ passed this test with ease. Never felt a “cringe”.

They also allowed me to sit for hours listening to music. They could just as easily been called Sittys for the effect. (Well, and because of the SIT).

The bass extension and control demonstrated that my room was not the problem than I thought. The bass was tight, fast and convincing. I still do have the desire for a sub to take it from 50 Hz down. and have on the bench Nelsons 6-24 crossover. Now to pick a sub to build or buy. The Ripole looked interesting but fear it will be a rabbit hole.

The Sissys’ most definitely add the “spooky” factor. Love when the hair on the back of my neck stands up and there is a tingle when listening to great female vocals, or exceptionally well recorded music.

So in my humble opinion the Sissys are gentlemanly, or gentlewomanly “beasts”. They are in control and I am glad they are. This has been a thoroughly enjoyable 48 hours.

Thanks to ZM for his tireless efforts and passion. Thanks to Papa. Our audio Buddha. And thanks to all who have given generously.
 

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well, yeah, Buddha is everywhere :clown:

now, you're officially spoiled

have no doubt (in fact, I know) that Harbeths are exquisite (if you like them yes - and I like them - being of same school as ReVox studio monitors, I spent many years with)

but- as you're spoiled now, to fulfill everything what A Class Fairy tale is bringing, you need to extend Harbeth quality to lower octaves

few 7-8" speaks are capable to do what decent 12" or 15" is able

so, either bigger speaks in general, or adding extra good subs
 
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sp33ls

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2018-04-06 7:09 pm
USA
Well. First impressions are that this this stupid spooky. :0

Honestly, setting the pots went without a hiccup, tho trying to access them with my super tight monoblock build was challenging. Managed to hit 199.5mV & 20mV without a problem. Let amp sit for 15m or so before setting offset. The LT4320 PSU boards deliver +/-26VDC to R+/R-.

PXL_20220501_004835830.MP.jpg

PXL_20220501_040822240.jpg

I can only hear a faint hum with my ear right next to the woofer (both channels). Honestly, I'm surprised that it's not more noticeable given my small chassis. I'm glad I went with shielded donuts, tho I'm wondering if I may be able to almost eliminate it completely by moving some wires around?

Also, I'm currently using a 3A fuse in line of each donut (as well as 2x 6AT at IEC). Was wondering if I need to bump that down to 2A5?

I'm very impressed with the bass out of this thing given it's 'only' 20-30W.

The organic tone and spooky realistic nature is reminiscent of some SETs, but with the added benefit of solid state bass. :)

Thanks for answering my numerous questions, as well as the creation of this beautiful beast Mighty ZM! And, of course, we must blame Pa for our greedy addiction. I'm super grateful that this community exists.
 
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Ben Mah

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2012-05-18 6:36 pm
Vancouver
Nice build.

Three suggestions for hum:

1. Twist each power transformer primary winding wires (red with black) together.

2. Twist V+, V-, Gnd wires together from power supply board to audio boards.

3. Rotate power transformers 90 degrees approximately from current position for minimum noise.
 
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sp33ls

Member
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2018-04-06 7:09 pm
USA
everything what Ben sez

and, routing mains wires under base plate, well, that's logical

and shown in all of my builds :rofl:

in rare cases of not having base plate ( custom/no Modu) I'm using screened leads to Donuts
Doh. Yeah honestly, I should've thought of that.
I can try to re-route my mains under the base plate, as well as add a screen if re-running cables doesn't solve it.

Would the SIT source/drain be susceptible to EMI from donuts?
 
Doh. Yeah honestly, I should've thought of that.
I can try to re-route my mains under the base plate, as well as add a screen if re-running cables doesn't solve it.
......

routing them under base plate is probably even better than screening

.....

Would the SIT source/drain be susceptible to EMI from donuts?


naah....
 
......

Also, I'm currently using a 3A fuse in line of each donut (as well as 2x 6AT at IEC). Was wondering if I need to bump that down to 2A5?

........


VA of Donut divided with mains voltage, then choosing first closest standard value of fuse, fast one

if you end with often popped fuse , increase to first next bigger standard value

all under condition that you have at least 10R NTC inrush limiter
 
Well. First impressions are that this this stupid spooky. :0

.......

I'm very impressed with the bass out of this thing given it's 'only' 20-30W.

The organic tone and spooky realistic nature is reminiscent of some SETs, but with the added benefit of solid state bass. :)
.......



well, one "just" needs to be realistic ...... most SET amps are ridiculously bad, and they're living and even gaining some cult status only because of two facts - it is realaaaaaaaaaaaaaaaaaly hard to rob tube of glorious midrange, and ppl are in most cases listening using eyes - reading periodicals and web tests, instead of using ears, with eyes closed

frankly, when I'm in mood, being up to task to make it properly, I can't pinpoint too much of difference between my sand amps and my vacuum amps; maybe reason is in fact that I'm making my vacuum amps sounding as my sand amps? :rofl:
dunno ...... but thing is that Pa spoiled me - I hate to be dependent of anyone, and really not doing anymore any construction to be oneandonlyintheworld; simpler explanation - my OCD is bothering me when using OPT made by someone else, and I'm clueless when building OPTs is in case
go figure

that being main reasons(s) why my tube playing is rare


..........

Thanks for answering my numerous questions, as well as the creation of this beautiful beast Mighty ZM! And, of course, we must blame Pa for our greedy addiction. I'm super grateful that this community exists.

yeah, blame Pa

my modest (as always :clown: ) contribution is that I'm just cheapskate, tried to involve cheap elevator parts in making knockout of his brilliant idea

no more than advanced Lego-assembler

:devilr:
 
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